The goal: In December, the electricity bill for Kathy Woody’s 1,600-square-foot home near La Mesa topped $400 — 30 percent more than what she usually paid. Boyfriend Brett Gardner vowed to help Woody cut her monthly power expenses.

Gardner has an advantage, because he’s an electrical engineer by trade. Also, he was already looking at ways to lower electricity use at Woody’s home. For instance, he had shut down the Jacuzzi and one of two 50-gallon water heaters in the house, which was custom-built in the 1950s with a second water heater to supply a photo-processing lab.

The process: Gardner started by pulling out old bills and looking at how often Woody reached the most expensive tiers of electricity.

“We were routinely in the third and fourth tiers above baseline” and paying additional surcharges, he said.

Gardner asked San Diego Gas & Electric Co. to test Woody’s meter to make sure it was correct. It was. So he bought a kilowatt meter online for about $25 and went around the house making a list of how much power each appliance and device used.

That led to other changes. “We had a lot of older fluorescent lights,” Gardner said. “I went around to every other bulb and popped them out. … I didn’t really notice a difference in the (overall) lighting” quality.

He also realized that three computers at Woody’s house were routinely on. These days, the couple turn on the computers only when they want to use them.

In addition, they got in the routine of completely shutting down their television and other entertainment gadgets so they wouldn’t draw power during standby mode.

Gardner looked into solar power but didn’t think the return on investment would be quick enough. Instead, he replaced the remaining electric water heater with a tankless gas model for about $2,000 after federal rebates.

The results: Gardner said the monthly electricity bill has dropped to about $65 thanks to factors such as energy-saving habits and use of power-stingy devices. He doesn’t expect Woody’s natural-gas bills to rise noticeably, because the new water heater is “on demand,” which means it’s not constantly consuming fuel to keep 50 gallons of water warm.

Woody probably will recoup her investment in the water heater in about a year, Gardner said.

“What you really want to look at is the long-term savings,” he said. “If you are saving $1,000 a year, multiply that by five, six or seven years — however long it’s going to last — and the savings are big.”